In one known electric motor construction, the first ends of two relatively rigid brush arms are pivotally mounted on an end cap and the opposite ends of a tension spring are connected to the second ends of the brush arms to urge these second ends towards the commutator. As a result, the brushes are suitably pressed into engagement with the commutator. However, installation of the brush arms is complicated, particularly if automated procedures are adopted. It is also normally necessary to fit insulators between the brush arms and the opposite ends of the tension spring, thus increasing the cost and adding to the difficulty of installing the brush arms.
To overcome these problems, it has been proposed, GB 987 375, to replace the tension spring with two blade springs pressed, respectively, from the two brush arms and arranged to engage the brush arm support means to urge the brush arms resiliently towards the commutator.
Another solution is to replace the relatively rigid brush arms with resiliently flexible brush leaf means. Brush leaf means of this form each comprise a first end, which is rigidly attached to a brush leaf support in the form of a terminal, and a contact portion. However, as a result of a manufacturing imperfections, it is impossible to ensure concentricity of an electric motor commutator or precise mounting of the first end of the brush leaf means. The brush leaf means must therefore be mounted so that the contact portion is resiliently urged towards the commutator and the brush leaf means must have sufficient resilient deformability to accommodate the maximum anticipated spacial discrepancies while maintaining adequate pressure between the commutator and the contact means incorporated in or supported by the contact portion of the brush leaf means.
One way to accommodate constructional tolerances is to provide brush leaf means of very thin material which can easily flex. However, in this case, the brush leaf means are not normally sufficiently robust and are not always capable of providing sufficient resilient loading on the commutator. An alternative solution is to form the brush leaf means of thicker material, but of greater length from a first, terminal end of the brush leaf means to the contact portion. However, the extent to which this solution can be applied is limited by the size of the electric motor and, normally, by the size of the end cap in which the brush leaf means are supported.
It has therefore been proposed to increase the effective length of the brush leaf means accommodated within a prescribed space by forming the brush leaf means as a plurality of sections which are connected to each other, but extend in different directions. Thus. as disclosed in GB 2 180 999, brush leaf means, for an electrodynamic machine, comprise a first resiliently flexible conductive section which has a first end, for fixed, non-pivotal attachment to a brush leaf support, and a second end; and at least one additional resiliently and independently flexible conductive section, which each have first and second ends, wherein the first end of each additional section is attached to the second end of another resiliently flexible conductive section; at least one said additional section extends in spaced relation to an adjacent resiliently flexible conductive section in a direction, from first end to second end, having at least a major directional component opposite the direction in which said adjacent section extends from the first end to the second end of said adjacent section; and one additional section has a free second end, to which no first end of any other additional section is connected, and a contact portion.
However, the construction disclosed in GB 2 180 999 is limited to brush leaf means in which the first resiliently flexible conductive section extends, from a first end to a second end, away from the contact portion and in which there is only one additional resiliently flexible conductive section. As a result, the first and second ends of the first resiliently flexible section are disposed on the same side of the contact portion. This arrangement imposes severe limitations on the effective length of the brush leaf means in that there is normally very little space between the support to which the first end of the first resiliently flexible conductive section is attached, and the outer enclosure of the electrodynamic machine.